1. Technical Field
The present invention relates to an apparatus, a method, and a test apparatus for detecting a change point of a signal under measurement.
2. Related Art
Japanese Patent Application Publication No. 6-94853 discloses a time measurement circuit that measures the timings of pulse edges. This time measurement circuit includes a counter that counts a clock, a latch that latches a value of the counter, a triangular wave generating circuit that generates a triangular wave in synchronization with the clock, an AD converter, and an adding device.
The latch acquires the counter value at the edges of the pulse under measurement. The AD converter samples the level of the triangular wave the edges of the pulse under measurement. The adding device outputs the edge timing of the pulse under measurement obtained by adding together the count value acquired by the latch and the output data of the AD converter. This time measurement circuit can accurately measure the edge timing of the pulse under measurement in less than one cycle of the clock.
However, since the high-speed and high-precision AD converter is expensive, the time measurement circuit using an AD converter as described above is also expensive. Many time measurement circuits are used in the field of test apparatuses, and therefore it is especially important to achieve a low-cost time measurement circuit with a simple configuration.